Re: about SFINAE usage

i wrote a template to test whether a type is a class type.
but i find that using an ordinary member function "test()" will cause
compiler error like"no qualified name for pointer to member".
what's the difference in this place???

template<typename T>
class ClassChecker{
    typedef char One;
    typedef struct{char _c[2];} Two;
    template<typename C> static One test(int C::*);
    template<typename C> static Two test(...);
public:
    enum{YES = sizeof(test<T>(0))==1};
    enum{NO = !YES};
};

template<typename T>
void CheckClass()
{
    if( ClassChecker<T>::YES )
        cout<<"type '"<<typeid(T).name()<<"' IS a Class type"<<endl;
    else
        cout<<"type '"<<typeid(T).name()<<"' IS NOT a Class type"<<endl;
}